1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device, and more particularly, to a method for manufacturing a liquid crystal display device using a liquid crystal drop method.
2. Discussion of the Related Art
A liquid crystal display device, among other ultra-thin flat panel display devices with a display screen having a thickness of several tens of cm, has a low operating voltage and low power consumption, and thus is ideally suited for portable applications, including in computers, as monitors, and military and aerospace applications.
Hereinafter, with reference to the accompanying drawings, a related art liquid crystal display device will be described.
As illustrated in FIG. 1, the related art liquid crystal display device comprises a lower substrate I and an upper substrate 3, which are opposite to each other. Although not illustrated in the drawings, TFTs and pixel electrodes are formed on the lower substrate 1, and a light shielding film, color filter layers, and common electrodes are formed on the upper substrate 3.
A liquid crystal layer 5 is formed between the lower substrate I and the upper substrate 3. The liquid crystal layer 5 is oriented in a designated direction by an orientation film (not shown) formed on the lower surface thereof.
A sealant layer 7 is formed between the lower substrate I and the upper substrate 3. The sealant layer 7 serves to seal the liquid crystal layer 5 and to bond the lower substrate 1 and the upper substrate 3 to each other.
The liquid crystal display device having the above structure is manufactured by a liquid crystal injection method or a liquid crystal drop method.
In the liquid crystal injection method, a lower substrate and an upper substrate are prepared, a sealant is deposited on one of the two substrates so that a sealant layer having an injection port is formed on the substrate, the substrates are bonded to each other and are bonded to by hardening the sealant layer, and liquid crystal is injected into a space between the bonded substrates through the injection port.
In the liquid crystal drop method, a lower substrate and an upper substrate are prepared, a sealant is deposited on the lower substrate so that a sealant layer without an injection port is formed on the lower substrate, liquid crystal is dropped on the lower substrate, and the two substrates are bonded to each other by hardening the sealant layer.
The liquid crystal injection method requires a long time to inject the liquid crystal, thus reducing productivity as substrate sizes increase. Accordingly, large-sized substrates use the liquid crystal drop method.
However, because the sealant layer is hardened under the condition that the liquid crystal layer is formed between the lower and upper substrates, the liquid crystal drop method causes domain defects due to a scattering of the orientation of the liquid crystal layer from high temperatures during hardening the sealant layer.
That is, in the liquid injection method, since the liquid crystal is injected into a space between the lower and upper substrates after the sealant layer is hardened, the liquid crystal layer is not exposed to high temperatures generated during hardening the sealant layer. However, in the liquid drop method, since the sealant layer is hardened after the liquid crystal layer is formed between the lower and upper substrates, the liquid crystal layer is exposed to high temperatures generated during hardening the sealant layer, and thus the orientation of the liquid crystal layer is scattered.